The measurement of enzyme activity in blood or plasma can be a useful detector and predictor of developing disease conditions and risk factors. Assays for blood and plasma enzyme activity that can be performed in a clinical setting may be used to rapidly determine which patients would receive, for example, an inhibitor in the case of pathological enzyme over-activity, or they may be used as diagnostic indices of tissue damage, disease pathology, or to detect the presence of toxic enzyme inhibitors.
Standard clinical chemical assays exist for measuring clinically-relevant enzyme activity or the presence of enzyme inhibitors. Some of these assays can measure the targeted enzyme activity by changing the amounts of NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) or NADH (reduced form of nicotinamide adenine dinucleotide) in a reaction mixture, whether directly or by additional reaction-mixture enzymes and substrates which couple the measurement of activity of a targeted enzyme to a change in NADH or NADPH. Currently, these assays use a color-change or other known detection methods to obtain their quantitative detection readouts. However, there is a need for detection reagents and methods that enable electrochemiluminescence (ECL) measurements of clinical chemistry enzyme activities, which can be used by coupling the cleavage of its disulfide bond to, for example, changes in NADPH, NADH, or a free sulfhydryl group, to provide the desired quantitative detection readout of enzyme activity.